The invention concerns a method for storing selected points of a nominal contour line plotted on the projection screen of a projection profile grinder for the control of the grinding wheel position when a profile corresponding to the nominal contour line is ground into a workpiece.
In a projection profile, grinder, the image of a grinding wheel, having a controllable position, and of a workpiece to be machined by it, in the engagement zone appears magnified via a projection beam on a projection screen over which a transparent overlay with a tracing of a nominal contour line is placed. By a suitable position control of the grinding wheel, for example, by means of a compound table, it is possible to control the grinding wheel in such a manner that the workpiece is ground according to the nominal contour line. This can be observed exactly on the screen, since in the ideal case, the boundary between dark (workpiece) and light (transmitted light) coincides with the nominal contour line.
For the grinding process, the respective position of the grinding wheel can be determined by an electronic control system, for example, a CNC system, which moves the holder of the grinding wheel, for example, via the slides of a compound table which are moved by servomotors.
Up until now, it has been customary to enter single control points numerically via a keyboard, a punched tape or of nominal contour line data. Data acquisition is extremely time-consuming in this process.
This invention is based on the objective to provide a method and device by means of which the input of a nominal contour curve into the control system of a projection profile grinder can be accelerated and its precision improved.
In a method of the type described initially, this objective is realized according to the invention by the fact that the image of a marker mounted on the holder of the grinding wheel projected on the projection screen is moved along the nominal contour line by moving the holder and the position of the holder is stored when the silhouette of the marker points to the selected points of the nominal contour line traced on the screen.
In a device for the realization of this process, the objective is achieved by the fact that a marker which can be imaged on the projection screen of the projection system is mounted on the holder for the grinding wheel of a projection profile grinder.
The marker has a precisely defined position relative to the engagement site of the grinding wheel, so that when the marker is imaged, for example, on the origin of the nominal contour line on the screen, the exact location of the grinding wheel relative to the origin of the profile actually to be machined into the workpiece is also known. Thus, by a precisely known displacement of the grinding wheel which corresponds to the distance between grinding wheel and marker, it is possible to move the grinding wheel exactly into the origin of the profile to be ground.
The same applies to any other point specifically identified on the nominal contour line, for example, by punching perforations on the overlay carrying the nominal contour line. As soon as the marker points to such a selected point on the screen, the position data of the overlay corresponding to this location are stored and this procedure is performed for a larger number of selected points along the nominal contour line until the important characteristics of the nominal contour line are stored in the form of numerical data in the control unit. With all of these data, it must be kept in mind that during recording the grinding wheel was still located a defined distance from the engagement site, but this additional displacement is the same in all points, so that it can be readily taken into account in the subsequent control of the grinding wheel.
The greatest advantage in this process in particular is that the high magnification of the projection beam allows an extraordinarily precise position determination of the carrier so that extremely high precision is obtained. Moreover, tracing of the nominal contour line can be realized very simply by manually adjusting the displacement of the carrier as is the custom of the operating personnel of projection profile grinders in the direct machining of workpieces.
It is of advantage for the marker to be movable between a first position in which it submerges in the beam path of the projection system and a second position in which it is removed from the beam path. In the second position, the marker therefore does not interfere with the machining process. Preferably the marker can be moved between the two positions by an electrical motor or a mechanical drive, where it is of advantage for this drive to be operable by the control system itself.
In a preferred practical version, provision is made for the marker to be a holder holding a transparent reticle with cross-hairs or a partially transparent or opaque disk with a small hole allowing transmission of the projection light and having a diameter of preferably 0.1 mm. This allows a particularly precise reading of the marker position on the screen; thus, with a magnification of 50.times. of the projection beam and a hole of 0.1 mm diameter in an opaque disk, the positioning precision obtained is in the order of 1-2 .mu.m.